Recursive data in JSON object

{
"groups": [
    {
        "name": "Event",
        "groups": [
            {
                "name": "Service",
                "subscriptions": [
                    {
                        "topic": "SERVICE_STATUS_PRESETS"
                    },
                    {
                        "topic": "AIRCRAFT_ACTIVATION",

                    },
                    {
                        "topic": "OUT_OF_SERVICE",

                    }
                ]
            }
        ]
    },
    {
        "name": "Enquiries",
        "groups": [
            {
                "name": "Service-related",
                "subscriptions": [
                    {

                        "topic": "PROMO_CODES_REQUESTS",

                    }
                ]
            }
        ]
    }
],
"subscriptions": [
    {
        "topic": "BANNERS",
    },
    {
        "topic": "DOCUMENTS",
    },
    {
        "topic": "USER",
    }
]

}

OK guys I have such JSON structure what I need is to: return all topics in array, in this example it will be:

[“SERVICE_STATUS_PRESETS”, “AIRCRAFT_ACTIVATION”, “OUT_OF_SERVICE”, “PROMO_CODES_REQUESTS”, “BANNERS”, “DOCUMENTS”, “USER”]

I try recursive calls like this, though I only get last three records:

getRecursive() {
if (Array.isArray(data)) {
       for (let i = 0; i < data.length; i++) {
         if (data[i].subscriptions) {
           return data[i].subscriptions.map((val: SubscriptionGroupDetails) => val.topic);
         } else if (data[i].groups) {
           return this.getAllTopics(data[i].groups);
         }
       }
     }
     if (data && data.groups) {
      return this.getAllTopics(data.groups);
     }
     return data.subscriptions.map((val: SubscriptionGroupDetails) => val.topic);
}

Answer

You could take a recursive approach and check

• if the handed over data is not an object for checking, then return with empty array,
• if the object has the wanted property, then return an array with the value of topic,
• or get the values and make a recursive call with the function and return an array with the result of it.

function getTopics(object) {
    if (!object || typeof object !== 'object') return [];
    if ('topic' in object) return [object.topic];
    return Object.values(object).reduce((r, v) => [...r, ...getTopics(v)], []);
}

var data = { groups: [{ name: "Event", groups: [{ name: "Service", subscriptions: [{ topic: "SERVICE_STATUS_PRESETS" }, { topic: "AIRCRAFT_ACTIVATION" }, { topic: "OUT_OF_SERVICE" }] }] }, { name: "Enquiries", groups: [{ name: "Service-related", subscriptions: [{ topic: "PROMO_CODES_REQUESTS" }] }] }], subscriptions: [{ topic: "BANNERS" }, { topic: "DOCUMENTS" }, { topic: "USER" }] },
    result = getTopics(data);

console.log(result);